The present invention relates generally to intravascular snare devices and systems and more particularly, devices which can be used to capture embolic material or thrombi found in blood vessels.
The intravascular snare device and system of the present invention is particularly useful when performing balloon angioplasty, stenting procedures, laser angioplasty or atherectomy in critical vessels where the release of embolic debris into the bloodstream can occlude the flow of oxygenated blood to the brain or other vital organs, which can cause devastating consequences to the patient. The snare device is also suited for the removal of clots adhering to vessel walls. While the snare device and system of the present invention is particularly useful in the cerebral vasculature and neurovasculature, the invention can be used in conjunction with any vascular interventional procedure in which there is an embolic risk.
A variety of non-surgical interventional procedures have been developed over the years for opening stenosed or occluded blood vessels in a patient caused by the build up of plaque or other substances on the wall of the blood vessel. Such procedures usually involve the remote introduction of the interventional device into the lumen of the artery, usually through a catheter. In typical carotid PTA procedures, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral artery and advanced, for example, through the vasculature until the distal end of the guiding catheter is in the common carotid artery. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guidewire sliding within the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient""s carotid vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
Another procedure is laser angioplasty which utilizes a laser to ablate the stenosis by super heating and vaporizing the deposited plaque. Atherectomy is yet another method of treating a stenosed blood vessel in which cutting blades are rotated to shave the deposited plaque from the arterial wall. A vacuum catheter is usually used to capture the shaved plaque or thrombus from the blood stream during this procedure.
In the procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass.operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. The stent is crimped tightly onto the balloon portion of the catheter and transported in its delivery diameter through the patient""s vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter.
Prior art stents typically fall into two general categories of construction. A first type of stent is expandable upon application of a controlled force, as described above, through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. A second type of stent is a self-expanding stent formed from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. Such stents manufactured from expandable heat sensitive materials allow for phase transformations of the material to occur, resulting in the expansion and contraction of the stent.
The above minimally invasive interventional procedures, when successful, avoid the necessity of major surgical operations. However, there is one common problem which can become associated with all of these types of procedures, namely, the potential release of embolic debris into the bloodstream that can occlude distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible that the metal struts of the stent can cut into the stenosis and shear off pieces of plaque which become embolic debris that can travel downstream and lodge somewhere in the patient""s vascular system. Pieces of plaque material can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream. Additionally, while complete vaporization of plaque is the intended goal during a laser angioplasty procedure, quite often particles are not fully vaporized and thus enter the bloodstream. Likewise, not all of the emboli created during an atherectomy procedure may be drawn into the vacuum catheter and, as a result, enter the bloodstream as well.
When any of the above-described procedures are performed in the carotid arteries, cerebral vasculature, or neurovasculature, the release of emboli into the circulatory system can be extremely dangerous and sometimes fatal to the patient. Naturally occurring debris can also be highly dangerous to a patient. That is, debris which travels through the blood vessel as a natural result of bodily functions and not as a result of an intervention procedure. Debris that is carried by the bloodstream to distal vessels of the brain can cause these cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Therefore, although cerebral percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been limited due to the justifiable fear of causing an embolic stroke should embolic debris enter the bloodstream and block vital downstream blood passages.
Medical devices have been,developed to attempt to deal with the problem created when debris or fragments that naturally occur or that enter the circulatory system following vessel treatment utilizing any one of the above-identified procedures. One approach which has been attempted is the cutting of any debris into minute sizes which pose little chance of becoming occluded in major vessels within the patient""s vasculature. However, it is often difficult to control the size of the fragments which are formed, and the potential risk of vessel occlusion still exists, making such a procedure in the carotid arteries a high-risk proposition.
In addition, the retrieval of fragmented clot may be incomplete, also resulting in emboli and distal occlusions, and further, access through tortuous lumens may prove difficult. Laser-based disruption devices employ the photo-acoustic effect to fragment clot. Local disruption may open up a proximal occlusion but also may cause significant distal emboli.
Other techniques which have been developed to address the problem of removing embolic debris include the use of catheters with a vacuum source which provides temporary suction to remove embolic debris from the bloodstream. However, as mentioned above, there have been complications with such systems since the vacuum catheter may not always remove all of the embolic material from the bloodstream, and a powerful suction could otherwise cause problems to the patient""s vasculature. Other techniques which have had some limited success include the placement of a filter or trap downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. However, there have been problems associated with conventional filtering systems as well. In particular, certain previously developed filtering devices do not optimize the area for embolic collection. That is, conventional filtering devices may not present a collection device that spans the entity of the vessel or it may include supporting structure that itself impedes emboli collection. Certain other devices do not embody sufficient angular resistance to collapse.
Moreover, thrombectomy and foreign matter removal devices have been disclosed in the art. However, in addition suffering from the same disadvantages as certain conventional filter devices, such devices have been found to have structures which are either highly complex or lacking in sufficient or effective expansion and retraction capabilities. Disadvantages associated with the devices having highly complex structure include difficulty in manufacturability as well as use in conjunction with microcatheters. Other less complex devices can pull through clots due to in part to the lack of experience in using the same or otherwise lack an expanded profile that is adequate in capturing clots or foreign bodies.
Furthermore, in current interventional radiology practice, the need arises to remove a variety of objects from intraluminal spaces. Among these are embolic coils, guidewire tips, distal catheter segments, thrombus and other vascular emboli, few of which can be readily removed with current devices. Thrombo-embolic materials can be friable, amorphous, and/or lubricious in nature contributing to this difficulty. Most current therapies rely on grasping, fragmenting, or dissolving the blood-based obstructions. Among the grasping devices are the loop snares and the wire basket snares. These devices may have limited effectiveness, due in part to the lack of encapsulation. Objects are difficult to grasp within these devices, and friable objects, e.g. blood-based blockages, tend to fragment when grasped or pulled, introducing multiple emboli.
Lytic drugs are also used to dissolve blood-based obstructions. These typically have the disadvantages of lengthy treatment/infusion times to remove the obstruction ( greater than 3 hrs.), production of emboli, and the potential for systemic iatrogenic bleeding as a side effect of the drug usage. Also, these drugs are not typically effective in removing obstructions that are not blood-based.
What has been needed is a reliable intravascular snare device and system for use when treating blood vessels. The snare devices should be capable of capturing any naturally occurring embolic debris or that which may be released into the bloodstream during an interventional treatment, while minimizing the area occupied by structure supporting the device, and safely containing the debris until the snare device is removed from the patient""s vasculature. The devices should embody an expanded profile that presents a consistent radial opening that completely occupies the vessel at the repair site as well as structure for effectively resisting collapse. Moreover, such devices should be relatively easy to deploy and remove from the patient""s vasculature and also should be capable of being used in narrow and very distal vasculature such as the cerebral vasculature. The following invention addresses these needs.
Briefly and in general terms, the present invention is directed towards snares for removing undesired material or objects and restoring patency of blood vessels. The snare is a linked or monolithic framework of thin struts that is radially expansible. The snare of the present invention embodies a structure that provides a consistent radial opening as well as improved radial and angular resistance to collapse. That is, as the device is pulled such as through a vessel, the entrance thereto will not fall back or tip over. Moreover, the snare device maintains clearance in its interior space along its length allowing the material or objects to enter and be captured.
In one aspect of the invention, the snare is manufactured from a tubular element to form struts (members run both generally longitudinally and generally circumferentially) with very small widths and thicknesses and rings (circumferential members) with very small widths and thicknesses but large expansion ratios. The body of the snare device is defined by a plurality of openings bounded by generally longitudinally and generally circumferentially extending members. A proximally extending member is attached to an elongate push member and the assembly is contemplated to be used in conjunction with a generally tubular delivery catheter.
Overall, the intent of the invention is to provide a structure that has the capacity to engage and retain naturally occurring or foreign bodies while having a minimal profile that can traverse easily and repeatably through a standard microcatheter across tortuous anatomy. The device embodies superior flexibility to be deployed and retrieved consistently across difficult anatomy while being able to retain captured material. The inner diameter of the device is heat-set to a pre-determined size. It is envisioned that there be a family of devices that have varying strut lengths, thicknesses, flexibility, and diameters as deemed appropriate for the specific type of vascular or non-vascular setting for which the device is to be used.
In a presently preferred embodiment, the snare device is self-expanding and includes a midsection that forms a generally tubular profile. The proximally extending member projects from a sidewall defining the generally tubular portion to thereby provide a substantially unobstructed radial opening at the proximal end of the snare. A terminal (i.e., distal) end of the snare device can be closed so as to form a pocket for receiving emboli or thrombotic debris. In the event it is desirable to employ a snare device manufactured from a tube embodying both proximal and distal open ends, a woven basket can be attached to the distal end of the device.
The cut tube snare device can assume a number of forms. In one presently contemplated aspect, the snare device of the present invention embodies first and second end portions, a pair of longitudinally spaced rings and a midsection defined by helically extending members. In another aspect, the intravascular snare device has a midsection defined by generally parallel longitudinally extending members. In other aspects, the snare device includes a single convoluted ring or alternatively a body defined by a truncated stirrup-like structure. In yet another embodiment, the snare device has a midsection including almond-shaped apertures as viewed perpendicular to the axis of the snare.
Moreover, the present invention embodies a tip for an endovascular device including an atraumatic soft coil for preventing damage to tissue and facilitates advanceability. The tip further includes multiple layers of coiled material to enhance these objectives as well as to provide stiffness variations.